In this project we are coupling genetic study of selected families and twin pairs, epidemiologic, immunologic, serologic and neurochemical studies. Disorders due to multiple factors include multiple sclerosis and Parkinsonism. This approach should clarify the etiology of these diseases, indicate individuals or populations at high risk and suggest mechanisms of prevention and treatment. To date, 14 presumptive "Multiple Sclerosis" families have been studied and 93 twin pairs with this condition have been ascertained and partially evaluated. A total of 48 Twin pairs with Parkinsonism have been ascertained and multidisciplinary evaluation instituted.